Electrical pick-up



July 24, 1934. N. STEIGMAN ELECTRICAL PICK-UP Filed Sept. 18, 1929INVENTOR I Israel N .fizelg'man Patented July 24, 1934 UNITED NT "OFFICEi 11,967,335)" I t V i g IsraelN. S teiginan, Brooklyn, NY. fApplication September 18; 1929, Serial Nb. 393,383

;j9 Claims (claim-1:00.41)

' This invention relates to electrical pickup; apparatus designed to"convert stimuli, sucheas sounds, movements, or mechanical vibrationsinto such pulsating 'electriccurrent as may be later broadcast,reproduced or recorded, and

' which correspond withoutmaterial'distortion to the originalsounds,-movements Qrvibrations. Such apparatus usually comprisesadynamo. or generator including'amagnet for generating a magneticfield,an'armature movable in the'field under the impulse of a stimulus, andcoils in whichcurrent is generated on the movement oi the armature. r s

As a particular applicationiof my. invention, my improvedapparatusmay-be used tomchange the mechanical vibrationsof a stylusoperating in the groove of a phonograph record, into: equivalentelectricalimpulses, or my apparatus may be used as a microphone? asdesired. The electrical output of the apparatus may later, be amplified,as for instance, by means of well known thermionic amplifiers, and madeto operate loud speakers or recording instruments, such as photnographs,telegraphones or thelike, orait may i f be used directly to modulatehighfrequencyv circuits for broadcasting purposes,-

ing means, such as, for example, springs ninterposed rubber members,cloth, or the like Such damping means not only causes material loss ofthe efiective power of the sti ulusoperating ,the'apparatus, whichpower, it is understood, is extremely minute in the first instance, butthe damping meanshas the additional defect of so restraining the freevibration :of the armature as to cause undesirable and often, grossdistortion of the reproduction, resulting in lack of correspondence,of==the output with the stimulus.

Distortion of reproduction-in previously known apparatus otthis typealsojoccurs gowing to. the

r fact that vibrationsat a certain frequency,;corresponding to thenatural frequency of vibration of the damping means, can be; imparted tothearmature more easily than otherifrequencies, which other frequenciesare therefore; transmitted with greater difficulty and are moreorlessirepressed, preventing faithfulreproduction, and resulting infurther diminution of the effective power of the stimulus, Furthermore,pickup apparatus heretofore in use has been not only mechanicallyrestrained by the damping means referredtto above, but the armaturesthereof have been of same means h'ave therefore been employed .justmeritof the predetermined area of tiguous armature and poler faces.

excessive Weight, due to the loading thereof with coils and otherdevices. The additional weight is enough to'resilst the free vibrationof the armature under the impulse "of the stimulus and is further,enough 'to cause undesirable wear of the parts and of the stimulus wherefor example, phonograph records are used as the transmitting medium."Finally, such weighted armatures are subject to the defect thatconsiderable energy in transmission is lost and consequent distortionoccurs due to the inertia of' the comparatively heavyfarmature, and theconsequent diificulty of starting and stopping the movement thercustomarily to correct the dlstortion caused by the aoove mentioned.defects. Said means has usually taken the form of electrical or. Wavefilf'ters for eliminating .or altering the undesirable portionsof theelectrical reproduced impulses or waves, but such filters result infurther undesirable absorption of energyQand are an experisiveandlinefficient means for approximating Ithej desired result.

invention contemplates the provision of a device, consisting merely. ofthe control and adthe con- My invention, further contemplates theprovision of means for so mountingrand vibrating'the armature of thepickup that the faces of said armature vibratein a plane substantiallyat right angles to the magnetic lines of force, and so that saidarmature is entirely free of mechanicalre- .straint against vibrationother than that 'due Ito its own weighhjaiidfrdm which springs anddamping means are entirely, eliminated, the arr'nature neverthelessbeing maintained in its prop- Her; position intl emagn etic field. Myinvention Ifurther' contemplates the provision of .an arma- Qture oiminimum weight whereby .the inertia thereof against free vibration isreduced to a minimum; with consequent maximum efficiency in faithfulreproduction and-with maximum utiliza- ,tionof the energyof thestimulusput thereon, so ,thatan extremely high..-degree of perfection of'reproductionmay be attainedwithout the necessity for,the,use ofwavefilters. ,My invention {further contemplates,the'iproduction or" asimple and comparatively inexpensive and efficient apmay also beoperated as a microphone, if desired.

The various objects of my invention will be clear from the descriptionwhich follows, and from the drawing, in which,

Fig. 1 is a perspective view of the preferred form of my improvedpickup, showing the device in use for the electrical conversion of soundin connection with a phonograph record.

Fig. 2 is a similar view of one of the magnet poles and of a portion ofthe armature therefor, showing a modified form of the pole and armaturefaces, the areas of which govern the degree of reluctance in themagnetic circuit, and therethrough govern the extent and characteristicsof the pulsations of the electrical output.

Fig. 3 is a diagrammatic view of my improved apparatus, showing themagnetic circuit therefor and showing, further, the connection thereofto a suitable amplifier means such as a thermionic" transformer.

Fig. 4 is a perspective view of a modified form of my apparatusillustrating a modified arrangement of the magnet poles and armature.

Fig. 5 is a similar view of the same, showing another modifiedarrangement.

Fig. 6 is a similar view of the same, showing a modified form ofarmature and showing the connection thereof to a suitable soundresponsive means whereby the apparatus may be used as a microphone, and

Fig. 7 is a similar view of another modified form of my apparatus,showing a different form of the faces of the pole pieces and armature.

Figure 8 shows a modified form of my device in which the armature pivotis mounted above the airgap.

In that practical embodiment of my invention which I have illustrated byway of example, in Fig. 1 a suitable magnet 10, which is preferably apermanent magnet, is provided with a pairof poles 11 and 12 which may bedisposed in various positions, as is shown in the remaining figures, andas will be more fully explained hereinafter. The magnet 10 may besecured or held in proper stationary position by means of a suitableextension 13 thereon, as may be found convenient or desirable.

Wound about the poles 11 and 12 and preferably spaced somewhat from thepreferably plane terminal faces 14 and 15 respectively thereof are thecoils 16 and 17 respectively, each composed of nal or other formpresenting two or more operative facets to the magnetic field induced bythe magnet 10. As illustrated, two facets 21' and 22 are provided on thepole face as 14 and two similar facets 25 and 26 are provided on thearmature face 19, though it will be understood that any desired numberof facets disposed on planes angularly arranged may be used instead, aswill be obvious to those skilled in the art and hence which need not beshown.

I prefer, however, that a single'groove only be made in each of thearmature and pole faces, and

that said groove be rectangular 'in cross-section,

though I do not desire to be understood as limiting myself to a singlegroove of any definite shape,

as above explained. As illustrated in Fig. 1, the width of the armature18 is very little less than the distance between the faces 14 and 15 ofthe adjacent poles, whereby the armature is arranged with the faces 19and 20 thereof as close as is physically possible to the respective polefaces 14 and 15. I prefer to so mount the armature that the gap betweenthe armature faces and the pole faces, while being of minimum extent, ispermanent as regards its width, and invariable for all practicalpurposes.

I further prefer to so mount the armature 18 that the faces 19 and 20thereof move in a path parallel to and across the pole faces 14 and 15and at afixed distance therefrom, and are constrained to move in thepath described substantially without mechanical restraint againstvibration in said path. Toward this end, the armature is pivoted about asuitable axis.

As shown in Fig. 1, I prefer to provide a nonmagnetic shaft as 29passing through part of the armature and spaced from the poles 11 and 12and terminating in conical bearings 30 mounted in suitable supports as31 secured to the magnet 10. A stylus as 32 may be secured to thearmature 18 on the opposite side of the pivot shaft 29 from that onwhich said poles are arranged, though it will be understood that thestylus may be on the same side of the shaft as are the poles, ifdesired. Said stylus may be held to the armature by means of a chuck 33secured by a suitable adjusting screw as 34. The stylus 32 is intendedto be inserted into the undulated track or groove 35 of the phonographrecord 36, whereby rotation of the record in the usual manner causes thestylus 32 to oscillate about the pivot shaft 29 under the impulse of thevariations in said track and thereby causes the armature faces tovibrate correspondingly, across and parallel to the pole faces.

No coils are provided on the armature so that the groove 35 has only aminimum amount of weight to move and the armature is free from restraintagainst vibration except that occasioned by the inertia due to its ownweight. This inertia, it will be seen, is also reduced to a minimum byreason of the simplicity of the armature and the possibility of reducingits weight to a minimum. Stops as 37 of non-magetic material may beprovided for limiting the vibratory movement of said armature, saidstops preferably projecting from the magnet 10 and being so spaced apartas to maintain the armature 18 at all times in the magnetic field of thepoles 11 and 12.

Should the armature therefore be subjected to an unusual force tendingto throw it completely out of the magnet field, the stops 37nevertheless maintain the'armature within the range of the magneticforce, which is sufficient to pull the armature back into its properposition without the necessity for using mechanical means such assprings or the like. In other words, the magnetic force in the field isthe agent serving to maintain the armature in its operative positionwithout other aid. 7

The coils 16 and 17 are suitably inter-connected as by means of theconductor 38 (Fig.

3), the terminal wires 39 ammo of said conductor being connected tosuitable amplifying apparatus 41, as willbe seen from Fig. 3.

The magnetic reluctance of the magnetic circuit may be varied bychanging the position of the armature in the magnetic field of thepoles,

by movement of the armature'across and substantially parallel to thepole faces and not from agaeasas pole to pole. By so varying themagnetic reluctance, a current varying in intensity and fre-- quency inexact correspondence to the vibration of the armature, is induc'edin the'coi1s 16.and 17 and may be used for thepurposes heretofore mentioned. aa i w. i

As illustrated in Fig.4, the armature42 isarranged across the ends ofthe magnet poles 43 and 44, the respective polefaces 45and 46 of whichare arrangedin thesame plane. Thepivoting shaft 47 for the armature maybe similar to the shaft 29, butonly' oneface as 48 ofthe armatureis'operative in this modification.

As shown in Fig. 5, the pole faces 49 and 50 of the'magnet 10 arearranged at substantially right angles to each other so that thesurfaces 51 and 52 of the armature 53are correspondingly arrangedalthough the operation thereofg'as above described, isnotmater'ially-altered. 4 i i As illustrated in Fig. 6, thearmature 54may be connected to the cone 55 or other suitable 'diaphragm by meansofthe connecting member 56, said cone or diaphragm being vibratory underthe impulse of sound waves. a n

The pole faces of the magnet 10 illustrated in Fig. 6 are shownsubstantially identical with those shown inFig; 4and therefore neednotbe further described. The armature '54, however, maybe pivoted on ashaft as 57 arranged parallel to the pole-"faces 45and 46; The vibrationof the armature across the pole faces without changing the width of thegap may be made to occur, however, in substantially the same wayirrespective of the arrangement-of the pivot therefor.

In Fig. 7, I have shown another form of mountingwhereby the armature 58may vibrate without change in the width of the gap. In this case,

the axis of the pivot shaft 59 lies in a plane perpendicular 'to theplane of themagnet 10, in distinction from the arrangements of the pivotshafts 29, 47 and 57, the axes of which lie in planes parallel totheplane of the magnet; This arrangement of the pivot shaft 59 necessitatestangular as in the other modifications.

Meansmay be provided for predetermining the characteristic of thecurrentinduced in the coils 16 and 17 on predetermined motion of anyofthe armatures 18, 42, 53, 54 and 58 across their'pole faces.

Said means may take the form of a multiplicity of facets as 21, 22, 25and 26form'ed bymaking one or more grooves as 23 and 24 in the polefaces and armature faces" respectively. illustrated in Fig."2', I preferthat said means take the form of a variationin the shape of theperiphery and extent of-the areas of the pole facets 64 and 65 and ofthe armature facets 66 and 67. The variation in said areas may beeffected by changing the shape of the sides of the grooves 68 and 69made in the magnet pole faces and in the armature faces, respectively,and consequently, in a change of the shapes of the sides 70 and '71 ofthe pole facets and of the sides 72 and '73 of the armature facets.

In other words, a variable change of area of the eifective armature andpole surfaces may result on movement of the armature through apredetermined angle in different positions of the of facetsare providedonthe pole faces.

armature. Ifz there- -were ino 'grooves in .the armature and' polefacesgand the width. of the pole, faces were-greater than-the maximumamplitude of vibration of. the armature; no current would be. induced inthe :.coils. vIf the sides of the grooves were vertical," then therewould. be a uniform variation in the current induced in the coils 3during a single movementof the arma' ture in one direction, butif thesides of the groove were straight "but inclined at'ani angle other thanaright angle to the. upper an'd lower faces. of the poles, then thevariationisuniformly variable. Again, if the sides of the groove: werecurved along predetermined lines, then the variation would be variablyvariable and1may:be predetermined to produce an output of the desiredcharacteristic, as. should be.c1ear' to those skilled in the art. Forexamplejtheburves .of thegroove sides 'may be. so designedsthat if. thearmature were to'swing through an angleoftwo degrees and during thatswing, to generate one volt, a

.swing of four degrees in the same direction might be caused to induceone and one half or five or and other number Of'VOltS, and not twovolts,

and a swing of sixdegrees might be caused to faces and armature facesand that said areas may.

bevaried as desired. As: shown in Fig. .7, the grooves 74 and75are"madetriangular-instead of rectangular, the grooves in all cases beingpreferably deep 1 enough to' prevent any. undesired passage of flux; Asshown in Fig. 8,- a multiplicity of grooves and aconsequent multiplicityThe pivot for the armature 81 is further arranged above the' pole'sinstead of belowthe poles as in Fig". 1 to give a somewhat greaterleverage.

It will also be se'enthatby providing an armature free of-coilsand'vibrating said armature so that the armature faces travel in a planesubstantially parallel to the faces of the poles orin a cylindricalsurface concentric with: thepolefaces,

I have produced a simple andefiicient mechanism operating 'with aminimum waste of energy and accurately responsive to the stimulusapplied theretofiwhereby efiicient "reproducion with a minimum ofdistortion becomes possible.

It willfurther be understood that while 1 preterm so pivot the armaturethat it moves as above described, the'armaturemay also be. pivoted soasto move atright angles'tothe described direction or acrbssthepolesfrom topto bottom, if desired, by merely changing the relative positionof the pivot on 'thearmature. T It will furtherb'e V understood thatwhile lg have shown a-record having a groove of one type, any type ofgrooved record may be used as a stimulus to the apparatus and that bymeans of a suitable diaphragm responsive to vibrations, my improvedapparatus may be used as a microphone, if desired.

While I have shown and described a preferred embodiment of my invention,it will be understood, further, that I do not wish to limit myselfthereto but intend to claim my invention as broadly as may be permittedby the state of the prior art and the terms of the appended claims.

I claim:

1. In an electrical pick-up, a magnet having poles thereon, relativelystationary coilson the poles, a movablesoft iron armature free of coilsand having multi-faceted faces thereon cooperating with the pole facesfor varying .the reluctance in the magnetic circuit of the magnet in avariably variable predetermined manner, and. means for pivotallysupporting the armature so that the faces of the armature remain at apredetermined distance from the pole faces during the vibration of thearmature in response to a stimulus, said means and the stimulus beingthe only mechanical forces other than said magnet acting upon thearmature tocause movement of the armature free from damping and lageffects.

2. In an electrical pickup device, .the combination with pole faces of amagnet of vibratory soft iron armature free of coils and having facesterminating in at least one edge curved in'the direction of its lengthcooperating with the pole faces and adapted to vary the reluctance inthe magnetic circuit of the magnet in a predetermined manner independentof the variation induced by the stimulus, and meansfor pivotallysupporting the armature so that the faces of the armature move in asurface parallel to the pole faces. g r

3. In an electrical pickup device, the combination with a pivotedarmature, of magnet poles serving as the sole means acting upon thearmature to swing it about its pivot into position to maintain it in themagnetic field of the poles, and means for pivotally supporting thearmature for vibration across the lines of force of the field and spacedfrom the poles to transmit to the armature substantially the full forceexerted by a stimulus thereon, and a stylus carried directly by thearmature. V,

4. In an electrical pickup device, the combina tion with a pivotedarmature, of magnetpoles serving as the sole means acting upon thearmature to swing it about its pivot into position to maintain it in themagnetic field of the poles, means for supporting the armature forvibration across the lines of force of the field and out of contact withthe poles, in response to a stimulus, and means for preventing thevibratory movement of the armature beyond predetermined limits.

5. In an electrical pickup device, the combination with means forinducing a magnetic field, means responsive to variations in themagnetic reluctance of the circuit for producing current, and means forvarying the reluctance of the circuit mounted for movement across thelines of force of said field and normally maintained in said fieldsolely bysaid first-mentioned means to utilize substantially the fullforce of a stimulus applied thereto, said reluctance varying meansincluding a pivoted armature provided with a series of spaced faceslying in the same warped surface, each of saidfaces having at least onelongitudinal edge thereof in the shape. of a curve of predetermined 4shape. 6. In an electrical pickup device, a magnet, grooved magnet polesthereon, coils on said poles adaptedto have currentinduced therein onthe variation ofthe magnetic reluctance in the field of said magnet, anarmature having grooved faces therein arranged at a predetermined fixeddistance from the faces of said poles, said armature being pivoted tomaintain said distance constant,,the effective area of the grooved polefaces and the armature faces being-predetermined by shaping theperipheral edges of said faces to control the characteristic of thecurrent induced in said coils.

- 7. In an electrical pick-up device adapted to be actuated by arevoluble phonograph record, a magnet having a pair of poles thereon,each of said poles having a reentrant recess to interrupt the faces ofsaid poles, the longitudinal edges of said recess being of predeterminedcurvilinear shape so that the pole surfaces beyond the recess are of.variable widths throughout their lengths, a coil wound about each ,polein spaced relation to the recess therein, a pivoted armature, a stylusadapted to engage the record carried by the armature, means forpivotally supporting the armature so that each face of the armature ismaintained at constant distance from the adjacent pole face, thearmature faces having recesses corresponding to and similar to therecesses of the pole faces.

8. In an electrical pick-up device, a magnet, a pair of pole piecesextending from the sides of the magnet toward each other and spacedapart,

an armature arranged in the space between said pole pieces, the innerend of each of said pole pieces having a re-entrant groove therein, andthe faces of the armature adjacent the pole faces having a similargroove therein and substantially the same shape and size as that of thecorresponding groove in the adjacent pole face, means for pivotallysupporting the armature for movement across the pole faces whilemaintaining the distance between the pole faces and the armaturefacesconstant, a vibratory member adapted to have a stimulus applieddirectly thereto carried by the armature, and a coil wound about each ofthepole pieces and connected to each other and arranged in spacedrelation to the grooves of said pole pieces.

9. In an electrical pick-up device, a U-shaped magnet, pole piecesextending toward each other from the sides of the magnet and spaced fromthe sides of the magnet, and a stylus carried by .the armature below thepivot, said pivot maintaining constant the spaces between the armaturefaces and the faces of the pole pieces.

ISRAEL N. .STEIGMAN.

